1. Field of the Invention
This invention relates in general to a furnace with a dual use inducer motor. More particularly, the invention relates to an improved furnace which allows for an inducer motor to operate at the proper speed for a furnace that is vented either vertically or horizontally.
2. Discussion of the Related Art
In conventional gas-fired forced air furnaces a thermostat senses the temperature in the comfort zone relative to a predetermined set point temperature. When the temperature is below the set point, the thermostat closes to supply thermostat ac power to the furnace as a call for heat. This initiates a sequence of events that ultimately causes the furnace to come on. An inducer motor is enabled to flow air through the heat exchangers for combustion, after which a gas valve is actuated to supply gas to the gas burners. An ignition device is also actuated to light the burners. A flame sensor then proves burner ignition. Then, after a predetermined blower delay time, which varies with furnace design, the furnace blower is actuated. The blower circulates room air from the return air duct over the furnace heat exchangers to pick up heat from the hot combustion products (carbon dioxide, nitrogen, oxygen, and water vapor). The heated circulating air then goes into the supply air plenum and is distributed by ductwork back to the living space. When the living space is warmed sufficiently to reach the thermostat set point, the thermostat terminates the call for heat. When this happens, the blower and burners go through a shut off sequence and the furnace awaits the next call for heat.
After passing through the heat exchanger, the combustion byproducts are vented outside of the structure through a vent pipe. The vent pipe can be oriented either predominantly horizontally through a side wall of the structure or predominantly vertically through the roof of the structure. When the inducer motor is in operation, a substantial step-up in pressure occurs between the intake of the inducer housing (the collector box) on the one hand, and the outflow of the inducer housing (the relief box) on the other hand. Typically there is negative pressure (relative to atmospheric pressure) at the intake. The pressure at the outlet of the inducer housing is slightly negative for conventional vertical vent systems, and substantially positive for horizontal side vent systems. A horizontally vented furnace is affected by wind conditions such that under certain outside conditions, such as high wind conditions, back pressure can cause the inducer to become overloaded. However, a vertically vented furnace is not affected as much by wind conditions because the buoyancy of the heated air and the angle of incidence of wind on the vent termination. In order to avoid a decrease in pressure drop across the inducer caused by wind in a horizontally vented furnace, the inducer system must be strong enough to overcome the back pressure.
Prior to the time the furnace is installed, it is not known whether the furnace will be vented horizontally or vertically. Therefore, in the past, in order to provide an adequately strong inducer motor, the motor would have to be sized for horizontal venting. If the furnace was installed with vertical venting, the motor would be oversized. An oversized inducer motor results in decreased efficiency and increased noise.
Recently, loopholes in the ANSI wind test for furnaces which many furnace manufacturers exploited to avoid the need for a stronger inducer system, have been closed. This further emphasizes two discrete operating regimes for vertical and horizontal venting. A stronger inducer system is now required to meet the revised standards. When this stronger motor is used in a vertically vented furnace, the loss of efficiency and increase in noise become highly undesirable. As furnace manufacturers submit new designs for certification under the revised test standards, inducer systems will be revised to produce greater overall capacity. These manufacturers will be manufacturing furnaces with inducer systems which, when vented vertically, will be greatly oversized. The present invention provides a solution to the problem of using an oversized motor in a vertically vented furnace.
An apparatus is provided for improving the efficiency and reducing the noise of a furnace. The present invention provides a two speed inducer motor which can be used as a single speed inducer for either a vertically or horizontally vented furnace. The inducer has a common terminal, a low speed terminal and a high speed terminal. In conventional two-speed furnace inducer systems, one lead is attached to each of the three terminals and the control automatically selects a speed. However, in the present invention, one lead is attached to the common terminal and, depending on whether the furnace is vented horizontally or vertically, either the high speed or low speed terminal is used. If the furnace is vented vertically, one lead is connected to the common terminal and the other lead is connected to the low speed terminal. Thus, the inducer system operates at a low speed when the furnace is vented vertically. If the furnace is vented horizontally, one lead is connected to the common terminal and the other lead is connected to the high speed terminal. Thus, the inducer system operates at the higher speed when the furnace is vented horizontally. This design approach allows, as a further benefit, the avoidance of cost associated with systems available from manufacturers with two-speed/two-stage furnaces.
These and other details, advantages and benefits of the present invention will become apparent from the detailed description of the preferred embodiment hereinbelow.